"use client";

import { useCallback, useEffect, useRef, useState, useSyncExternalStore } from "react";
import { fetchUserSettings } from "@/lib/api/domains/settings-api";
import {
  fetchGitHubWorkspaceSettings,
  updateGitHubWorkspaceSettings,
} from "@/lib/api/domains/github-api";
import { createQueuedUserSettingsSync } from "@/lib/user-settings-sync";
import { hasUserSettingsSyncFailure } from "@/lib/user-settings-sync-failure";

const STORAGE_KEY = "kandev:github-presets:v1";
const MIGRATED_KEY = "kandev:github-presets:migrated-to-backend:v1";
const WORKSPACE_MIGRATED_KEY_PREFIX = "kandev:github-presets:migrated-to-workspace:v1:";
const SYNC_FAILED_KEY = "kandev:github-presets:sync-failed:v1";

export type SavedPreset = {
  id: string;
  kind: "pr" | "issue";
  label: string;
  customQuery: string;
  repoFilter: string;
  createdAt: string;
};

export function readStorage(): SavedPreset[] {
  if (typeof window === "undefined") return [];
  try {
    const raw = window.localStorage.getItem(STORAGE_KEY);
    if (!raw) return [];
    const parsed = JSON.parse(raw) as unknown;
    if (!Array.isArray(parsed)) return [];
    return parsed.filter(
      (p): p is SavedPreset =>
        typeof p === "object" &&
        p !== null &&
        typeof (p as SavedPreset).id === "string" &&
        ((p as SavedPreset).kind === "pr" || (p as SavedPreset).kind === "issue") &&
        typeof (p as SavedPreset).label === "string",
    );
  } catch {
    return [];
  }
}

function writeStorage(presets: SavedPreset[]) {
  if (typeof window === "undefined") return;
  try {
    window.localStorage.setItem(STORAGE_KEY, JSON.stringify(presets));
  } catch {
    /* ignore quota / access errors */
  }
}

// External store: single source of truth shared across all hook consumers.
const listeners = new Set<() => void>();
let snapshot: SavedPreset[] | null = null;
const emptySnapshot: SavedPreset[] = [];

function getSnapshot(): SavedPreset[] {
  if (snapshot === null) snapshot = readStorage();
  return snapshot;
}

function getServerSnapshot(): SavedPreset[] {
  return emptySnapshot;
}

function subscribe(cb: () => void) {
  listeners.add(cb);
  return () => {
    listeners.delete(cb);
  };
}

function publish(next: SavedPreset[]) {
  snapshot = next;
  writeStorage(next);
  for (const l of listeners) l();
}

function readServerPresets(value: unknown): SavedPreset[] | null {
  if (!Array.isArray(value)) return null;
  return value.filter(
    (p): p is SavedPreset =>
      typeof p === "object" &&
      p !== null &&
      typeof (p as SavedPreset).id === "string" &&
      ((p as SavedPreset).kind === "pr" || (p as SavedPreset).kind === "issue") &&
      typeof (p as SavedPreset).label === "string",
  );
}

async function readLegacyServerPresets(): Promise<SavedPreset[] | undefined> {
  try {
    const response = await fetchUserSettings({ cache: "no-store" });
    return readServerPresets(response.settings.github_saved_presets) ?? [];
  } catch {
    return undefined;
  }
}

const syncServer = createQueuedUserSettingsSync<SavedPreset[]>(SYNC_FAILED_KEY, (next) => ({
  github_saved_presets: next,
}));

let workspaceSyncQueue = Promise.resolve();

function syncWorkspaceSavedPresets(workspaceId: string, next: SavedPreset[]): Promise<void> {
  workspaceSyncQueue = workspaceSyncQueue
    .catch(() => undefined)
    .then(() =>
      updateGitHubWorkspaceSettings({
        workspace_id: workspaceId,
        saved_presets: next,
      }).then(() => undefined),
    );
  return workspaceSyncQueue;
}

function snapshotKey(value: SavedPreset[]): string {
  return JSON.stringify(value);
}

function hasMigratedToBackend(): boolean {
  if (typeof window === "undefined") return false;
  return window.localStorage.getItem(MIGRATED_KEY) === "1";
}

function markMigratedToBackend(): void {
  if (typeof window === "undefined") return;
  try {
    window.localStorage.setItem(MIGRATED_KEY, "1");
  } catch {
    /* ignore storage failures */
  }
}

function hasMigratedToWorkspace(workspaceId: string): boolean {
  if (typeof window === "undefined") return false;
  return window.localStorage.getItem(WORKSPACE_MIGRATED_KEY_PREFIX + workspaceId) === "1";
}

function markMigratedToWorkspace(workspaceId: string): void {
  if (typeof window === "undefined") return;
  try {
    window.localStorage.setItem(WORKSPACE_MIGRATED_KEY_PREFIX + workspaceId, "1");
  } catch {
    /* ignore storage failures */
  }
}

export function __resetSnapshotForTests() {
  snapshot = null;
  for (const l of listeners) l();
}

function useLegacySavedPresetsSync(enabled: boolean) {
  useEffect(() => {
    if (!enabled) return;
    let cancelled = false;
    const initialKey = snapshotKey(readStorage());
    fetchUserSettings({ cache: "no-store" })
      .then((response) => {
        const serverPresets = readServerPresets(response.settings.github_saved_presets);
        if (cancelled || !serverPresets) return;
        const local = readStorage();
        if (snapshotKey(local) !== initialKey) return;
        if (hasUserSettingsSyncFailure(SYNC_FAILED_KEY)) {
          void syncServer(local);
          return;
        }
        if (serverPresets.length === 0 && local.length > 0 && !hasMigratedToBackend()) {
          void syncServer(local);
          markMigratedToBackend();
          return;
        }
        publish(serverPresets);
        markMigratedToBackend();
      })
      .catch(() => {});
    return () => {
      cancelled = true;
    };
  }, [enabled]);
}

function useWorkspaceSavedPresets(workspaceId: string | null) {
  const [workspacePresets, setWorkspacePresets] = useState<SavedPreset[] | undefined>(undefined);
  const writeSeq = useRef(0);
  useEffect(() => {
    if (!workspaceId) {
      setWorkspacePresets(undefined);
      return;
    }
    let cancelled = false;
    const seq = writeSeq.current;
    setWorkspacePresets(undefined);
    fetchGitHubWorkspaceSettings(workspaceId)
      .then(async (settings) => {
        if (cancelled || seq !== writeSeq.current) return;
        const serverPresets = readServerPresets(settings.saved_presets) ?? [];
        let local: SavedPreset[] | undefined = readStorage();
        if (local.length === 0) {
          local = await readLegacyServerPresets();
        }
        if (cancelled || seq !== writeSeq.current) return;
        if (
          serverPresets.length === 0 &&
          local !== undefined &&
          local.length > 0 &&
          !hasMigratedToWorkspace(workspaceId)
        ) {
          setWorkspacePresets(local);
          void syncWorkspaceSavedPresets(workspaceId, local)
            .then(() => markMigratedToWorkspace(workspaceId))
            .catch(() => {});
          return;
        }
        setWorkspacePresets(serverPresets);
        if (local !== undefined || serverPresets.length > 0) {
          markMigratedToWorkspace(workspaceId);
        }
      })
      .catch(() => {
        if (!cancelled) setWorkspacePresets(undefined);
      });
    return () => {
      cancelled = true;
    };
  }, [workspaceId]);
  const setWorkspacePresetsFromLocal = useCallback((next: SavedPreset[]) => {
    writeSeq.current += 1;
    setWorkspacePresets(next);
  }, []);
  return { workspacePresets, setWorkspacePresets: setWorkspacePresetsFromLocal };
}

export function useSavedPresets(workspaceId: string | null = null) {
  const presets = useSyncExternalStore(subscribe, getSnapshot, getServerSnapshot);
  const { workspacePresets, setWorkspacePresets } = useWorkspaceSavedPresets(workspaceId);
  useLegacySavedPresetsSync(!workspaceId);
  const activePresets = workspaceId ? (workspacePresets ?? []) : presets;

  const save = useCallback(
    (input: Omit<SavedPreset, "id" | "createdAt">) => {
      if (workspaceId && workspacePresets === undefined) return null;
      const preset: SavedPreset = {
        ...input,
        id: `p_${Date.now().toString(36)}_${Math.random().toString(36).slice(2, 8)}`,
        createdAt: new Date().toISOString(),
      };
      const next = [...activePresets, preset];
      if (workspaceId) {
        setWorkspacePresets(next);
        void syncWorkspaceSavedPresets(workspaceId, next)
          .then(() => markMigratedToWorkspace(workspaceId))
          .catch(() => {});
        return preset;
      }
      publish(next);
      void syncServer(next);
      markMigratedToBackend();
      return preset;
    },
    [activePresets, workspaceId, workspacePresets, setWorkspacePresets],
  );

  const remove = useCallback(
    (id: string) => {
      if (workspaceId && workspacePresets === undefined) return;
      const next = activePresets.filter((p) => p.id !== id);
      if (workspaceId) {
        setWorkspacePresets(next);
        void syncWorkspaceSavedPresets(workspaceId, next)
          .then(() => markMigratedToWorkspace(workspaceId))
          .catch(() => {});
        return;
      }
      publish(next);
      void syncServer(next);
      markMigratedToBackend();
    },
    [activePresets, workspaceId, workspacePresets, setWorkspacePresets],
  );

  return { presets: activePresets, save, remove };
}